The present application is generally directed to the field of linear or curvilinear ultrasonic transducers, particularly those used in medical imaging.
Ultrasonic imaging has been utilized for a number of years in the medical field. Linear and curvilinear ultrasonic transducers are used to produce visual images of features within a patient""s body. Such ultrasonic imaging transducers are also used in other fields. However, medical imaging is perhaps the best known use of such transducers.
Typically, an ultrasonic transducer for producing visual images of features inside the body includes an array of ultrasonic elements which may be driven by a desired excitation and/or receive ultrasonic reflections obtained from various features of interest.
As technology progresses, there has been an increasing need to produce ultrasonic images having enhanced resolution. There is also, of course, a desire to produce ultrasonic transducers producing not only better images, but exhibiting greater reliability and ease of manufacture.
In a typical ultrasonic transducer array, a piezoelectric crystal is driven by a voltage applied across first and second piezoelectric electrodes. Such an ultrasonic transducer is generally formed of a piezoelectric crystal that is provided with first and second piezoelectric electrodes to form a electrode crystal assembly. This electrode crystal assembly is then fastened to a backing, and the piezoelectric crystal with its associated piezoelectric electrodes is then cut transversely into individual electrode elements extending along a longitudinal direction.
One of the limiting factors in manufacturing such piezoelectric ultrasonic transducers is that, as transducer elements size decreases, the difficulty in affixing contact wiring to the transducer increases. Such contact wiring is needed to connect the acoustic transducer with its associated drive or sensing circuitry.
According to the teachings of the present application, a double sided flexible circuit, flex circuit or connector is used to contact both of the electrodes used to drive or sense a vibration within the piezoelectric crystal. According to the teachings of the present application, the first and second piezoelectric electrodes are connected to the flexible double sided circuit or connector either by soldering the flexible double sided connector to the piezoelectric electrodes or alternatively through the use of anisotropic conductive adhesive. When the flexible double sided connector is bonded to the piezoelectric electrodes, a fillet in the bonding material is used to strengthen the connection. In the case of a soldering method, this fillet would of course be a solder. However, this fillet could additionally be formed of a conductive epoxy by screen printing or another process. Anisotropic conductive adhesive may also be used to connect the flexible connector to the transducer.
In one preferred embodiment, one of the first and second connector conductors is a common conductor commonly connected to all of either the first and second piezoelectric electrodes. The second connector conductor is, in this case, however, constructed of a plurality of individual conductors each connected to an individual piezoelectric transducer element. In an alternative embodiment, individual grounds are used and accessed to individually drive or sense from each of the piezoelectric transducer elements. Thus, both sides of the flexible double sided connector contains individual electrodes for connecting to each of the piezoelectric elements.
In yet another embodiment, piezoelectric transducer element density can be increased by utilizing two flexible double sided connectors, connecting to the piezoelectric electrodes of the piezoelectric crystal from two sides. This enables each connector conductor of the double sided flexible connector to access only every other piezoelectric transducer element, thereby increasing the spacing or pitch of the conductive wirings provided on the flexible double sided connector to enable the pitch of the individual conductors on each flexible double sided connector to be reduced. Thus, the relative spacing of each connector wire as compared to its transducer element is increased. This can be done in two ways. Registration can be maintained between the first and second conductive contacts so that the two contacts of a single piezoelectric element are addressed from a single flexible circuit or double sided connector. Alternatively, it may be desirable to offset the first and second sides from each other in a single flexible double sided connector, so that each circuit element is contacted using a first flexible double sided connector and the second terminal is contacted using a second flexible double sided connector.
Through the use of individual grounds in accordance with the teachings of the present application, alternative piezoelectric elements may desirably have their grounds on opposite planes of the piezoelectric crystal. This may serve to reduce noise, for example, depending upon the driving system employed.
There are several other features of the present application which result in improved transducer. A concave lens having a transmission velocity substantially greater than water may be used to focus the transducer, particularly in the transverse direction. This lens is constructed in the preferred embodiment of an epoxy having a transmission velocity of greater than 1700 m/sec. In contrast, water has a transmission velocity of about 1500 m/sec. A shielding layer is desirably deposited outside of the piezoelectric crystal, associated matching layers, and acoustic lens. This shielding layer reduces electromagnetic interference as well as electrically shielding the patient from the sensor. By properly sizing the thickness of the shielding layer, the shield may attenuate electromagnetic radiation interference without substantially attenuating ultrasonic signal sensitivity. Desirably, this shield layer is vapor deposited to provide 100% coverage of the top surface and side walls of the transducer. The transducer of the present application further includes distended portions of the acoustical element, shielding layer and protective cover which extend over the side walls of the piezoelectric crystal and matching layers to protect the seams there between, including the adhesive binding the piezoelectric crystal to the backing and matching layer.
It should be apparent that the above features and advantages of the present invention filed from the preferred embodiments set forth here and below, as may be understood from the following description and accompanied drawings which illustrate exemplary embodiments of the present invention.